The present invention relates in general to wind energy plants, and, more particularly, to storm protection of wind energy plants.
Changing the pitch, or angle, of air foil type propellers for speed regulation has long been in use for preventing overspeeding in normal winds and light storms. However, most of such governing devices, if they change the pitch sufficiently to prevent overspeeding in winds above 50 to 60 miles per hour, when the blade angle to the wind is increased beyond a certain point in order to prevent any further increase in speed, the outer portion of the propeller begins to act as a high speed centrifugal "paddle" fan. Back pressures of 100 miles per hour or more are thus created against the back portions of the propeller and this "back pressure" in turn allows tremendous pressure buildup against the front side of the revolving propellers, often breaking them as well as subjecting the entire plant and tower to severe storm damage. Winds exceeding 100 miles per hour are encountered at the tops of towers, and a successful wind energy system must be automatically controlled when such storms strike.
The inventors of the hereinafter disclosed invention also have patents relating to wind energy plants having the propeller axis offset from the vertical. Such patents include U.S. Pat. No. 4,068,131. Furthermore, the present inventors also have patents wherein the mast of a wind electric plant is offset from the center of the gear assembly, see, e.g., U.S. Pat. No. 4,088,420.
While the devices disclosed in the just-mentioned patents afford protection to the wind energy plant in storms wherein wind velocities do not exceed about 60 miles per hour, and are thus adequate under most conditions, there are storms in which wind velocities exceed 60 miles per hour, especially at the heights of the propellers of the wind energy power plants. As used herein, the term "high winds", or the like, will refer to wind velocities with respect to the wind energy plant of about 60 miles per hour and above. Even though such storms are rare in many areas, even the slimmest possibility of such a storm should be accounted for.
A drawback to presently known wind energy power plants is that protection against high winds, that is, winds in excess of 60 miles per hour, is either not possible at all, or can be accomplished only at considerable expense. Accordingly, all known wind energy power plants either are not protected against high winds, or are protected inadequately, or are extremely expensive.
During storms, ice may form on the plant propeller blades creating a severe unbalance. The rotational velocities of the blades in a typical wind power plant are such that blade unbalance can set up severe vibrations in the plant. These vibrations can be serious enough to damage or even destroy a plant unless the plant is shut down. Known plants have no means of automatically shutting down the blades in a manner which, itself, does not present a possibility of damaging the plant. A shutdown which is too rapid may cause severe damage to the plant. As ice formation on propeller blades is a possibility in storms in many areas, and in some storms in all areas, complete storm protection for wind energy plants should account for this contingency, yet known plants do not, and thus have serious drawbacks.
Yet a further drawback to known plants is the uncontrolled manner in which manual shutdown can be effected. If the manual shutdown is not controlled properly, it is possible for an operator, either through inexperience or panic, or the like, to shut down the plant too rapidly in a storm condition, thereby causing the plant to be severely damaged, if not destroyed, due to the wind pressure placed on the blades as they slow down. Thus, complete storm protection for a wind energy plant should provide control over manual shutdown so that operation also is protected.
There is, therefore, a need for a means of protecting wind energy power plants against high winds which is reliable, yet inexpensive and easily installed.
There is also a need for a device which automatically shuts down a plant in a controlled manner if that plant is being subjected to excessive vibration, and which controls plant manual shutdown.